Lipid Organization in Mixed Lipid Membranes Driven by Intrinsic Curvature Difference

Area of Science:

• Membrane biophysics
• Lipid self-assembly
• Materials science

Background:

• Understanding lipid organization in mixed membranes is crucial for cell function.
• Oxidized lipids can alter membrane properties and organization.
• Phospholipid mixtures exhibit complex phase behaviors.

Purpose of the Study:

• To investigate the lateral organization of mixed lipid membranes containing an oxidized lipid, 1-palmitoyl-2-glutaryl-sn-glycero-3-phosphocholine (PGPC).
• To determine how PGPC interacts and segregates with three common bilayer lipids: DPPC, DOPC, and POPC.
• To elucidate the role of lipid shape and membrane curvature in driving lipid segregation.

Main Methods:

• Laurdan fluorescence spectroscopy to probe lipid packing and order.
• Novel spectral fitting to quantify emission components.
• Dynamic light scattering to determine aggregate sizes and membrane curvature.

Main Results:

• All PGPC mixtures exhibited two distinct fluorescence emissions, indicating phase separation or distinct domains.
• DPPC/PGPC mixtures showed component separation into vesicles and micelles at higher PGPC concentrations.
• POPC/PGPC mixtures displayed random mixing at low PGPC fractions, transitioning to component separation at higher fractions.
• DOPC/PGPC mixtures consistently separated into vesicles and micelles.
• Lipid segregation was attributed to differences in intrinsic molecular curvature, influenced by tail saturation and truncation.

Conclusions:

• Lipid segregation in mixed membranes is driven by intrinsic molecular shape and resulting membrane curvature.
• PGPC's inverse-cone shape facilitates mixing with similarly shaped POPC but not with cone-shaped DOPC or DPPC in certain phases.
• The study provides insights into the fundamental principles governing lipid organization and phase behavior in complex biological membranes.